The present invention relates to a room temperature-curable organopolysiloxane composition or, more particularly, to a room temperature-curable organopolysiloxane composition which is outstandingly free from the disadvantage in working therewith that the uncured composition as applied sags down by the gravity to lose the once-shaped desired form.
Various types of room temperature-curable or vulcanizable organopolysiloxane compositions (referred to as RTV composition hereinbelow) are known and widely used as a sealing or caulking material, coating material and adhesive in the fields of building construction and mechanical and electrical industries by virtue of their excellent properties. While an uncured RTV composition, capable of being cured into a rubbery elastomer by standing in a moisture-containing atmosphere at room temperature, usually has a pasty consistency susceptible to deformation or flow under an outer force, it is essential that the RTV composition is free from the problem of sagging in the absence of outer forces excepting gravity when it is used as a sealing material in buildings and instruments. Conventional products of RTV compositions are more or less not free from this problem so that most of RTV compositions are prepared with admixture of a sagging-reducing agent to reduce, if not completely, this undesirable phenomenon.
Several kinds of sagging-reducing agents are known to be effective in silicone RTV compositions. For example, U.S. Pat. No. 4,100,129 teaches the use of a trifunctional organopolysiloxane of high phenyl content and a fumed silica filler in combination although this method is questionable in respect of the effectiveness of the method despite the expensiveness of the special organopolysiloxane. An alternative method is known in which a surface-treated fumed silica filler is used as a sagging-reducing agent, optionally, in combination with the above mentioned trifunctional high-phenyl organopolysiloxane. If not to mention the relative expensiveness of the surface-treated fumed silica filler, this method is also not free from the problem of the increased elastic modulus or decreased rubbery elasticity of the cured RTV composition to cause fracture of the sealing or insufficient sealing effect when it is used as a sealing material because the desired sagging-reducing effect can be obtained only by compounding a relatively large amount of the filler.
It is also known that addition of a polyoxyalkylene compound to RTV compositions is effective in reducing sagging of the composition (see, for example, Japanese Patent Kokai No. 56-853). A problem in this method is the bleeding of the additive on the surface of the cured RTV composition as a result of the high mobility of the polyoxyalkylene in the organopolysiloxane composition so that the adhesive strength between the cured RTV composition and the substrate surface may sometimes be unduly low to cause peeling of the cured composition from the substrate surface.